1. Field of the Invention
The present invention relates to a disk drive apparatus of the type in which a recording disk is fitted on a rotor hub which is driven to rotate.
2. Description of the Related Art
A disk drive apparatus has been known in which recording disks such as hard disks are mounted on the outer periphery of a rotor hub of a spindle motor. In this type of disk drive apparatus, as disclosed in the U.S. Pat. No. 4,814,652, a hard disk fitted on the rotor hub is carried by a radial extension of the rotor hub and a spacer is placed on the hard disk. Then, a plurality of hard disks and spacers are alternately stacked and fitted on the rotor hub and the stack is finally clamped by a clamp member fixed to the rotor hub. The clamp member is fixed to the upper face of the rotor hub by means of screws at its portion which is radially inside the inner peripheral edges of the hard disks.
In this known structure, the thickness or axial dimension of the disk drive apparatus is inevitably increased due to the presence of the portion of the clamp member radially inside the inner peripheral edge of the hard disk and due to the necessity for the margin of the axial length of the rotor hub which is required for forming the threaded holes. In addition, distortion or warp of the hard disks tends to be caused due to, for example, uneven tightening of the screws for fixing the clamp member.
In order to obviate this problem, an attempt has been made in which the inner peripheral edge of the clamp member and the outer peripheral edge of the rotor hub are threaded so that the clamp member is screwed onto the rotor hub, thereby clamping the hard disks. This arrangement eliminates the necessity for the provision of the portion of the clamp member radially inside the inner peripheral edge of the hard disk, as well as the necessity for formation of threaded holes on the top of the rotor hub, thus remarkably reducing the axial length or thickness of the disk drive apparatus.
The reduction in the axial thickness of the disk drive apparatus also reduces the axial length of the mating portions of the rotor hub and the clamp member. Consequently, fine screw threading has to be conducted both on the inner peripheral surface of the clamp member and the outer peripheral surface of the rotor hub, which is difficult to carry out. Formation of such fine screw threading is extremely difficult particularly when the axial length of the mating region between the rotor hub and the clamp member is small, e.g., 1 mm or so.
The disk drive apparatus of the kind described also employs a labyrinth type seal for preventing bearing lubricant from being scattered to the exterior, thus avoiding contamination of the hard disks and other portions. The sealing effect for preventing external scattering of lubricant will be enhanced by reducing the gap between the rotating part and the seal member and by arranging a greater number of seal members in stages. The reduction in the gap size and increase in the number of the seal members, however, requires a high degree of machining precision, with the result that the cost of production is raised correspondingly. This problem is critical when the axial thickness of the disk drive apparatus is reduced, particularly when the axial thickness is less than 6 mm, more specifically less than 5 mm.